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    SubjectRe: sata promise and software raid5...
    You need to test all the disks running at once, this should give a much
    clearer picture of how the system will perform with a raid volume. a
    simple test is like so:

    -> hdparm -t /dev/sda2 & hdparm -t /dev/sdc2 & hdparm -t /dev/sdc2 &
    hdparm -t /dev/sdd2

    This will get them all going at once, but may jumble the output a bit.

    Evan


    On Wed, May 26, 2004 at 03:46:57AM +0400, Andrey Nekrasov wrote:
    > Hello,
    >
    > controller - Promise SATA 150 TX4, linux 2.6.7-rc1-bk1, HDD Maxtor
    > 250Gb (x4)
    >
    > Why so slowly reads (and writes) with software raid5?
    >
    > gnome:~ # hdparm -t /dev/sda2
    >
    > /dev/sda2:
    > Timing buffered disk reads: 148 MB in 3.01 seconds = 49.16 MB/sec
    > gnome:~ # hdparm -t /dev/sdb2
    >
    > /dev/sdb2:
    > Timing buffered disk reads: 148 MB in 3.02 seconds = 49.01 MB/sec
    > gnome:~ # hdparm -t /dev/sdc2
    >
    > /dev/sdc2:
    > Timing buffered disk reads: 148 MB in 3.03 seconds = 48.90 MB/sec
    > gnome:~ # hdparm -t /dev/sdd2
    >
    > /dev/sdd2:
    > Timing buffered disk reads: 144 MB in 3.00 seconds = 47.96 MB/sec
    > gnome:~ #
    > gnome:~ #
    > gnome:~ # hdparm -t /dev/md0
    >
    > /dev/md0:
    > Timing buffered disk reads: 64 MB in 3.12 seconds = 20.52 MB/sec
    > gnome:~ #
    >
    >
    > gnome:~ # cat /etc/raidtab
    > raiddev /dev/md0
    > raid-level 5
    > nr-raid-disks 4
    > nr-spare-disks 0
    > persistent-superblock 1
    > parity-algorithm left-symmetric
    > chunk-size 1024
    >
    > device /dev/sda2
    > raid-disk 0
    >
    > device /dev/sdb2
    > raid-disk 1
    >
    > device /dev/sdc2
    > raid-disk 2
    >
    > device /dev/sdd2
    > raid-disk 3
    >
    >
    > bye
    > --
    >
    >
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